Vault is a Hunting Demon Hunter skill unlocked at Level 9. The Demon Hunter vaults forward at high speed, moving as a shadow with a flair for acrobatics.
This is the Demon Hunter's movement ability and one of the most effective movement/escape skills in the game.
The Demon Hunter melts into the shadows, using them to spin forward with a series of acrobatic somersaults and flips.
 Skill Rune Effects
See the Vault rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
The following Demon Hunter passives provide a benefit to Vault, runed or not:
 Skill Design
I could do that...if I wanted to.
Every character in Diablo III has at least one movement ability. The Demon Hunter has several with Vault the most obvious and fastest.
With a click the Demon Hunter vaults a considerable distance in the blink of an eye, passing right through monsters. Vault can be used repeatedly, with no cool down, Discipline permitting.
Can not pass through Monsters'
Evasive Fire can however pass through Waller's walls.
Vault was first shown at BlizzCon 2010 as one of the originals when the Demon Hunter was unveiled. Wyatt Cheng had this to say about it:
This a movement skill. The Barbarian has Leap Attack, the Wizard has Teleport and we wanted to make sure all our classes had a way to get around the battlefield. In this skill we wanted to sell the Shadow theme. Initially we talked about Shadow Vault and stuff like that, but we decided to just call it Vault and let the art peak for itself. There's no need to have to weave these concepts into every single skill. The artistic representation has some acrobatics and has some shadow themes to it. It's basically a way to take a solid mechanic and wrap it up with the aesthetic we are trying to sell and deliver something we think will be fun for the players.
Flux also weighed in on the skill from his time on the BlizzCon 2010 demo:
Vault was the last Demon Hunter skill the pre-made demo characters had, and it was useful to rush through the dungeon or to escape from boss packs. It was a fast moving cartwheel that covered about 1/2 the screen. It’s seen a few times in the DH cinematic. This skill allows the DH to pass through any monsters in the way, though it’s stopped by obstacles such as walls or doors or the huge, chopping cleaver booby traps that filled this year’s demo dungeon.
Skill tiers were removed shortly before the beta started in September 2011, and Vault became a level 6 skill. The skill system was once again overhauled for the Beta Patch 13, and Vault was classified as a Defensive skill and moved up to level 13. For Beta Patch 14, it was re-classified as a Hunting skill and dropped to level 9. The "Hunting" category replaced "Shadow".
The skill animations for Vault were modified slightly during the beta. Initially both genders of Demon Hunter vaulted in a cartwheel animation. Someone must have decided this wasn't macho enough for the male though, since his Vault became a sort of sideways flipping leap, without any hand planted on the ground, pre-release.
Vault can be seen in action on video here:
You can find pictures in the Diablo III screenshot and picture gallery:
The Demon Hunter mid-Vault.
Another shot of the multiple shadows.
Each shadow has its own posture.
By now, you should be sick of the word 'vault'.